Optimisation of simple and regenerative organic Rankine cycles using jacket water of an internal combustion engine fuelled with biogas produced from agricultural waste

Abstract

Internal combustion engines have a very important place in biogas production facilities to convert biogas energy to electricity. Unfortunately, although intense studies on improving internal combustion engine efficiencies by operational optimisation methods, serious progress is not achieved yet. However, there are many ways to improve the performance of these engines apart from structural optimisation methods. One of the most important ways is to utilize by integrating jacket water used to cool the biogas fuelled internal combustion engines into the new generation low-temperature heat recovery systems like organic Rankine cycles. In the present study, simple and regenerative organic Rankine cycles were optimised to improve the overall performance of an biogas fuelled internal combustion engine by using the jacket water which is released into the atmosphere after cooling the engine. Also, the energy, exergy and environmental aspect of these systems are evaluated. Finally, exergoeconomic analysis for both systems are conducted, and then payback periods of both systems are determined. As a result of the study, the maximum net power, thermal and exergy efficiencies of the simple organic Rankine cycle was calculated as 42.14 kW, 11.47 % and 63.27 % respectively, while the maximum net power, thermal and exergy efficiencies of the regenerative organic Rankine cycle are found as 45.3 kW, 12.34 % and 68.02 %. In addition, it is observed that the maximum power production obtained from the regenerative organic Rankine cycle corresponded to nearly 630 kg CO2/h emission reduction. The best payback period value is also calculated as 7.37 years in the simple organic Rankine cycle.